FIG. 1 is a block diagram illustrating an exemplary network structure of a universal mobile telecommunications system (UMTS).
Referring to FIG. 1, the universal mobile telecommunications system (UMTS) comprises a user equipment (UE), a UMTS terrestrial radio access network (UTRAN), and a core network (CN). The UTRAN includes at least one radio network sub-system (RNS) and each RNS includes a radio network controller (RNC) and at least one base station (e.g., Node B) managed by the RNC. The Node B comprises at least one cell.
FIG. 2 is an architectural diagram illustrating a radio interface protocol between a UE and a UTRAN based on the 3GPP (3rd Generation Partnership Project) radio access network specifications.
Referring to FIG. 2, the radio interface protocol horizontally includes a physical layer, a data link layer, and a network layer. The radio interface protocol vertically includes a user plane for data information transfer and a control plane for signaling transfer. The protocol layers in FIG. 2 may be divided into L1 (first layer), L2 (second layer), and L3 (third layer) based on the lower three layers of the open system interconnection (OSI) standard model, for example.
The layers depicted in FIG. 2 are described below. The physical layer, as the first layer, provides an information transfer service to an upper layer using physical channels. The physical layer is connected to a medium access control (MAC) layer above the physical layer via transport channels through which data are transferred between the medium access control layer and the physical layer. Data is transmitted between different physical layers, and more particularly, between the physical layer of a transmitting side and the physical layer of a receiving side via physical channels.
The medium access control (MAC) layer of the second layer provides services to a radio link control layer above the MAC layer via logical channels. The radio link control (RLC) layer of the second layer supports reliable data transfer and is operative in segmentation and concatenation of RLC service data units (SDUs) sent down from an upper layer.
A radio resource control (RRC) layer located on the lowest part of the third layer is defined in the control plane only and controls the logical channels, the transport channels, and the physical channels with configuration, reconfiguration, and release of radio bearers (RBs). In this case, the RB includes a service offered by the second layer for the data transfer between the UE and the UTRAN. Generally, configuring RB defines the characteristics of protocol layers and channels necessary for providing a specific service and establishes respective specific parameters and operational methods.
A multimedia broadcast/multicast service (MBMS) is described below. An MBMS offers a streaming or background service to a plurality of UEs using a downlink dedicated MBMS bearer service. An MBMS is provided during one session, and data for the MBMS is transmitted to the plurality of UEs via the MBMS bearer service during an ongoing session only. A UE performs activation first for receiving the MBMS to which the UE has subscribed and receives the activated services only.
The UTRAN provides the MBMS bearer service to at least one UE using radio bearers. The radio bearers used by the UTRAN include point-to-point radio bearers and point-to-multipoint radio bearers. The point-to-point radio bearer is a bi-directional radio bearer and is configured by a logical channel DTCH (dedicated traffic channel), a transport channel DCH (dedicated channel), and a physical channel DPCH (dedicated physical channel) or a physical channel SCCPCH (secondary common control physical channel). The point-to-multipoint radio bearer is a unidirectional downlink radio bearer and is configured by a logical channel MTCH (MBMS traffic channel), a transport channel FACH (forward access channel), and a physical channel SCPCH. The logical channel MTCH is configured for each MBMS offered to one cell and is used for transmitting user-plane data of a specific MBMS to a plurality of UEs.
A logical channel MCCH (MBMS control channel), as shown in FIG. 3, is a point-to-multipoint downlink channel and is used in transmitting control information associated with the MBMS. The logical channel MCCH is mapped to the transport channel FACH (forward access channel), while the transport channel FACH is mapped to the physical channel SCCPCH (secondary common control physical channel). A cell has one MCCH only.
FIG. 3 is a diagram illustrating a point-to-multipoint radio bearer (RB).
Referring to FIG. 3, the point-to-multipoint RB is a uni-directional RB that comprises a logical channel (MTCH: MBMS Traffic CHannel) and a transport channel (FACH: Forward Access CHannel), and a physical channel (SCCPCH: Secondary Common Control Physical CHannel). The logical channel MTCH is configured for each MBMS service provided to a single cell, and is used for transmitting user plane data of a particular MBMS service to a plurality of users.
The UTRAN that provides MBMS service transmits, to a plurality of terminals, a MBMS-related control message (e.g., a RRC message related to MBMS service data) via a MCCH (MBMS Control CHannel). Examples of an MBMS-related message include a message that informs MBMS service data, and/or a message that informs point-to-multipoint RB data. Referring to FIG. 12, the logical channel MCCH is a point-to-multipoint downlink channel that maps to a transport channel FACH (Forward Access CHannel), which, in turn, maps to a physical channel SCCPCH (Secondary Common Control Physical CHannel). For a single cell, only one MCCH exists.
A terminal wishing to receive a particular MBMS that uses a point-to-multipoint RB first receives, via the MCCH, a RRC message that includes RB data. The point-to-multipoint RB is then established with the terminal using such RB data. Thereafter, the terminal continues to receive the physical channel SCCPCH (e.g., the channel to which the MTCH is mapped) and obtains the data of the particular MBMS service being transmitted via the MTCH.
When one session of a particular MBMS service that uses a point-to-multipoint RB is completed, the UTRAN transmits a message that instructs the release of the point-to-multipoint bearer, via the MCCH to the terminals that are receiving the particular MBMS service. Also, the UTRAN releases the point-to-multipoint RB established at the RNC and Node B. Meanwhile, a terminal that has received the above-identified message releases the point-to-multipoint RB that had been established with the terminal for the particular MBMS service.
While a particular MBMS service is in progress, one or more sessions for that service may occur in sequence. In such case, a session may be defined in various ways. For example, a session may be each complete episode of a multi-episode drama or a session may be certain portions of a sports program, such as scenes that show goals in a soccer match, for example.
When data to be transmitted for a particular MBMS service is generated at the MBMS data source, the core network (CN) informs a session start to the RNC. In contrast, when there is no further data at the MBMS data source to be transmitted for a particular MBMS service, the core network (CN) informs a session stop to the RNC. Between the session start and the session stop, a data transfer procedure for the particular MBMS service may be performed. In such case, only those terminals that have joined a multicast group for the MBMS service may receive data that is transmitted by the data transfer procedure.
In the above session start procedure, the UTRAN that received the session start from the core network (CN) transmits an MBMS notification to the terminals. In such case, MBMS notification refers a function of the UTRAN for informing a terminal that the transmission of data for a particular MBMS service within a certain cell is impending. The UTRAN may use the MBMS notification procedure to perform a counting operation that determines the number of terminals that wish to receive a particular MBMS service within a particular cell. The counting procedure is used to determine whether the radio bearer for providing the particular MBMS service should be set as point-to-multipoint (p-t-m) or point-to-point (p-t-p). To select the MBMS radio bearer, the UTRAN internally establishes a threshold value. After performing the counting function, the UTRAN may set a point-to-point MBMS radio bearer if the number of terminals existing within the corresponding cell is smaller than the threshold value, and may set a point-to-multipoint MBMS radio bearer if the number of terminals existing within the corresponding cell is greater than or equal to the threshold value.
If a point-to-point radio bearer is to be set, the UTRAN allocates a dedicated logical channel to each terminal (UE) and sends the data of the corresponding service. If a point-to-multipoint radio bearer is to be set, the UTRAN uses a downlink common logical channel to send the data of the corresponding service.
FIG. 4 is a diagram illustrating a channel configuration in a UE side for a multimedia broadcast/multicast service (MBMS). FIG. 5 is a diagram illustrating a transmission scheme of MCCH (MBMS control channel) information.
Referring to FIG. 5, the UTRAN providing an MBMS service transmits the MCCH information to a plurality of UEs via the MCCH channel. The MCCH information is periodically transmitted according to a modification period and a repetition period. The MCCH information is categorized into critical information and non-critical information. The non-critical information may be freely modified each modification period and/or each repetition period to be transmitted. The modification of the critical information, however, may only be made at each modification period. Thus, the critical information is repeated one time in each repetition period. However, the modified critical information is only transmitted at a start point of the modification period.
Referring to FIG. 4, the UTRAN periodically transmits a physical channel MICH (MBMS notification indicator channel) to notify whether the MCCH information is updated during the modification period. Accordingly, a UE attempting to receive only a specific MBMS does not receive the MCCH or MTCH until a session of the service begins but receives the MICH periodically. The update of the MCCH information refers to a generation, addition, modification or removal of a specific item of the MCCH information.
Referring again to FIGS. 4-5, once a session of a specific MBMS begins, the UTRAN transmits an NI (notification indicator) through a MICH, which is an indicator of notifying to receive an MCCH channel, to a UE attempting to receive the specific MBMS. The UE having received the NI via the MICH receives an MCCH during a specific modification period indicated by the MICH.
The MCCH information is control information (e.g., RRC messages) associated with an MBMS, and includes MBMS modification services information, MBMS non-modification services information, MBMS point-to-multipoint RB information, and/or access information.
A UE attempting to receive a specific MBMS using a point-to-multipoint radio bearer receives MCCH information including radio bearer information via an MCCH and then configures the point-to-multipoint radio bearer using the received information. After completion of configuring the point-to-multipoint radio bearer, the UE keeps receiving a physical channel SCCPCH to which an MTCH is mapped, to acquire data of the specific MBMS transmitted via the MTCH.
A UTRAN may transmit MBMS data discontinuously via the MTCH. In so doing, the UTRAN periodically transmits a scheduling message via an MSCH (e.g., SCCPCH carrying MTCH), to which an MTCH is mapped, to UEs. The scheduling message informs a transmission start timing point and transmission period of MBMS data transmitted during one scheduling period. For this, the UTRAN previously informs the UE of a transmission period (e.g., a scheduling period) of scheduling information.
When the UTRAN transmits the above-described messages for a specific MBMS, an MBMS service identifier and/or an MBMS transmission identifier for identifying the specific MBMS is included in the message. The MBMS transmission identifier comprises an MBMS session identifier and an MBMS service identifier. For example, when the MBMS modification services information message is transmitted, an MBMS transmission identifier and services information corresponding to the MBMS transmission identifier is included in the message to be transmitted.
If a frequency layer convergence scheme is used in an MBMS and cells using different frequencies are overlapped each other, the UTRAN may make the MBMS provided in cells using a specific frequency. The cells using the specific frequency for the MBMS are called a preferred layer (e.g., PL). A method making UEs receive the MBMS converged into the cells included in a PL is called a frequency layer convergence (FLC) scheme. The FLC scheme may be used in both a hierarchical cell structure (HCS) and a non-hierarchical cell structure. FLC information includes a target frequency (e.g., a frequency of PL) and an offset applied during determining a cell.
However, in the conventional method, when the UTRAN includes information for a plurality of services in a message to be transmitted, MBMS service identifiers and/or MBMS transmission identifiers and information for all the services are included in the message. This causes the volume of the message to increase and may result in waste of radio resources.